Light-emitting device having a roughened surface with different topographies

ABSTRACT

This invention provides an optoelectronic semiconductor device having a rough surface and the manufacturing method thereof. The optoelectronic semiconductor device comprises a semiconductor stack having a rough surface and an electrode layer overlaying the semiconductor stack. The rough surface comprises a first region having a first topography and a second region having a second topography. The method comprises the steps of forming a semiconductor stack on a substrate, forming an electrode layer on the semiconductor stack, thermal treating the semiconductor stack, and wet etching the surface of the semiconductor stack to form a rough surface.

CROSS-REFERENCE TO OTHER APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.12/230,054, now U.S. Pat. No. 7,834,369, entitled “Light-Emitting DeviceHaving a Roughened Surface With Different Topographies”, filed Aug. 22,2008, which claims the right of priority based on Taiwan ApplicationSerial Number 096131320, filed Aug. 23, 2007, which are hereinincorporated by references.

TECHNICAL FIELD

This invention relates to a semiconductor optoelectronic device having arough surface and the manufacturing method thereof.

BACKGROUND OF THE DISCLOSURE

Surface roughening is one of the efficient ways to improve lightextraction efficiency of a light-emitting device. Roughening thesubstrate or the upmost semiconductor layer into irregular protrusionsldepressions to scatter incident light impinging on the roughened surfaceis an example to improve light extraction efficiency. Roughening surfacecan be achieved by known processes like mechanically polishing orreactive-ion-etching (RIE). Another feasible way is performed by wetetching the wafer immersed in an etching solution for certain duration.The surface is roughened by different etching rates of the etchingsolution versus different exposed crystal planes of the surface. Theroughened surface of the light-emitting device, as shown in FIG. 1, isformed by wet etching. The light-emitting device comprises a growthsubstrate 11, an n-type semiconductor layer 12, an active layer 13, ap-type semiconductor 14, a p-side conductive pad, and an n-sideconductive pad. The surface of the p-type semiconductor layer 14 iswet-etched to form a roughened surface. An undercut 17 is formed due tolateral etching in the border between the p-side conductive pad 16 andthe p-type semiconductor layer 14. The contact area between the p-sideconductive pad 16 and the p-type semiconductor layer 14 is thereforereduced such that the device reliability is easily failed or the p-sideconductive pad 16 is easily peeled off by the stress. Besides, theuniformity of the roughened surface formed by the conventional wetetching method is not good enough to keep the product stable.

Another conventional way to prevent the light-emitting device fromreliability failure or pad peeling is to form the roughened surfacebefore forming the conductive pad, but the contact resistance betweenthe conductive pad and the roughened surface of the underlying layerbecomes high and therefore downgrade the device performance. Besides,the resulted surface of the conductive pad is uneven and thereforeobstructs the wire-bonding yield.

SUMMARY OF THE DISCLOSURE

One aspect of the present invention is to provide an optoelectronicsemiconductor device comprising a substrate; a semiconductor stackfurther comprising a first semiconductor layer of a first conductivity,an active layer, and a second semiconductor layer of a secondconductivity; and an electrode layer formed on the second semiconductorlayer; wherein the first and/or second semiconductor layer having arough surface comprising a first region having a first topography and asecond region having a second topography.

Another aspect of the present invention is to provide a method forforming a rough surface on a semiconductor layer of an optoelectronicsemiconductor device. The method comprises the steps of forming asemiconductor stack on a substrate; forming an electrode layer on thesemiconductor stack; heat treating the semiconductor stack and theelectrode layer; and wet etching the surface of the semiconductor stackto form a rough surface.

The optoelectronic semiconductor device comprises light-emitting deviceor photovoltaic device.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram showing a light-emitting device accordingto a conventional structure.

FIG. 2A to FIG. 2B are schematic diagrams showing one embodiment of alight-emitting device in accordance with the present invention.

FIG. 2C is a schematic diagram showing the top view of thelight-emitting device in FIG. 2A or FIG. 2B.

FIG. 3A is an SEM picture showing the first topography of the roughsurface formed in accordance with the present invention.

FIG. 3B is an SEM picture showing the second topography of the roughsurface formed in accordance with the present invention.

FIG. 4 is a flow chart showing the manufacturing method in accordancewith the present invention.

FIG. 5A to FIG. 5C are schematic diagrams showing a light-emittingdevice comprising a bonding structure in accordance with the presentinvention.

FIG. 6 is a schematic diagram showing a light-emitting device comprisinga lateral structure in accordance with the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 2A to FIG. 2C show a light-emitting device 2 in accordance with thepresent invention. FIG. 2C is a top view of the light-emitting device 2,and FIG. 2A and FIG. 2B are the cross-section views along with AA′ andBB′ respectively. As shown in FIG. 2A and FIG. 2B, the light-emittingdevice 2 comprises a substrate 21 having a top surface and a bottomsurface; a first semiconductor layer 22 of a first conductivityoverlaying the substrate; an active layer 23 overlaying the firstsemiconductor layer 22; a second semiconductor layer 24 of a secondconductivity comprising a rough surface overlaying the active layer 23;an extended electrode layer 25 overlaying the second semiconductor layer24; a first conductive pad 26 overlaying a portion of the extendedelectrode layer 25 and a portion of the second semiconductor layer 24;and a second conductive pad 27 underlying the bottom surface of thesubstrate 21. The material of the first semiconductor layer 22, theactive layer 23, or the second semiconductor layer 24 comprises n-typeor p-type AlpGaqIn(I_p_q)p or AlxInyGa(I_x_y)N (O˜p, q, x, y˜I; (p+q)˜I;(x+y)˜1). The first semiconductor layer 22 comprises a firstconductivity type cladding layer, and the second semiconductor layer 24comprises a second conductivity type cladding layer. The extendedelectrode layer 25 is a current spreading layer having a patternextended toward the surroundings of the light-emitting device forspreading current as shown in FIG. 2C. The first conductive pad 26 is abonding pad covering and electrically coupled to a portion of theextended electrode layer 25. The material of the extended electrodelayer 25 comprises single or multilayer of metal or metal alloy such asGelAu. The material of the conductive pad 26 comprises multilayer ofmetal such as Cr/Au. In one embodiment, the light-emitting device 2further comprises an ohmic contact layer 28 interposed between thesecond semiconductor layer 24 and the extended electrode layer 25. Theohmic contact layer 28 comprises a semiconductor layer with a higherdoping concentration than that of the second semiconductor layer 24,such as GaAs having Si-doping concentration higher than 10^(18cm-3)· Theconductivity type of the ohmic contact layer 28 can be the same as ordifferent to the second semiconductor layer 24 and form an ohmic contactwith the second semiconductor layer 24. In a preferred embodiment, theohmic contact layer 28 is formed only under the region covered by theextended electrode layer 25. The first conductivity type comprisesn-type or p-type, and the second conductivity type is different from thefirst conductivity type.

The rough surface comprises a first region 241 having a first roughtopography and a second region 242 having a second rough topography. Thefirst region and the second region comprise a plurality of depressionsand protrusions. The dimension of the first rough topography is smallerthan that of the second rough topography. In an embodiment of thepresent invention, the distance between the neighboring depressions orthe distance between the neighboring protrusions of the first roughtopography is around 0.1 to 0.5 micron. The depth of at least one of thedepressions or the height of at least one protrusion of the first roughtopography is around 0.1 to 0.5 micron. The distance between theneighboring depressions or the distance between the neighboringprotrusions of the second rough topography is around 1 to 10 microns.The depth of at least one of the depressions or the height of at leastone of the protrusions of the second rough topography is around 0.5 to 2microns. The first rough topography as shown in FIG. 3A is a randomlyrough surface having a plurality of depressions and protrusions. Thesecond rough topography as shown in FIG. 3B is a wave-shape surface. Thesecond region 242 having the second topography is adjacent to andsurrounds the extended electrode layer 25, and therefore separating theextended electrode layer 25 from the first region 241 having the firstrough topography. The level, i.e, the average altitude of the surface,of the second region 242 is about 0.5 to 2 microns lower than that ofthe first region 241. The cross-sectional shape of the second region 242is a curve such that the interface between the extended electrode layer25 and the second region 242 is outward oblique from the extendedelectrode layer 25 to prevent from undercut and further improve thereliability of the device and the peeling-off issue of the electrodelayer.

FIG. 4 discloses a manufacturing method for forming the above-mentionedlight-emitting diode 2. The method comprises the steps of:

-   1 providing a growth substrate 21;-   2 forming a first semiconductor layer 22, an active layer, and a    second semiconductor layer 24 sequentially on the growth substrate;-   3 forming an extended electrode layer 25 on the second semiconductor    layer 24; proceeding a thermal treatment step, such as rapid thermal    annealing (RTA);-   4 forming a first conductive pad 26 on a portion of the extended    electrode layer 25 and the second semiconductor layer 24;-   5 proceeding a thermal treatment step, such as rapid thermal    annealing (RTA);-   6 wet etching the second semiconductor layer 24 by an etching    solution comprising HF, HN03, CH3COOH, and iodine under a low    temperature condition from room temperature to 60° C. to form a    rough surface thereon, wherein the features of the rough surface is    described in the previous embodiments, such as FIG. 3A and FIG. 3B;-   7 forming a second conductive pad 27 on the other side of the    substrate 21.

The structure formed by the method is shown in FIG. 2A or FIG. 2B.

FIG. 5A shows another embodiment of the present invention. The light-emidevice 5 a as shown in FIG. 5A is similar to the light-emitting device2. The distinction is that the substrate 51 of the light-emitting device5 a is a conductive substrate. The substrate 51 can also be atransparent or opaque conductive substrate. It is also preferred thatthe substrate is a conductive substrate comprising a material havinghigh thermal conductivity not lower than 100 W/crn.oC, such as Si, Cu,or diamond. The conductive substrate 51 is coupled to the firstsemiconductor layer 22 by a conductive connecting layer 52. Theconductive connecting layer 52 comprises a transparent conductive layeror a conductive adhesive layer. The material of the transparentconductive layer comprises transparent conductive oxide, such as indiumtin oxide (ITO), zinc oxide (ZnO), or thin metal. The material of theconductive adhesive layer comprises silver paste or solder metal. Thelight-emitting device 5 a further comprises a reflecting layer 53 formedbetween the conductive connecting layer 52 and the first semiconductorlayer 22 for reflecting the light emitted from the active layer 23 andpreventing from being absorbed by the conductive substrate 51 if theconductive substrate 51 is opaque.

The manufacturing method for forming the light-emitting device 5 acomprises the steps of:

-   -   1 providing a growth substrate (not shown);    -   2 forming a first semiconductor layer 22, an active layer 23,        and a second semiconductor layer 24 sequentially on the growth        substrate;    -   3 bonding a temporary substrate (not shown) to the second        semiconductor layer 24;    -   4 removing the growth substrate to expose one surface of the        first semiconductor layer 22;    -   5 forming a reflecting layer 53 on the exposed surface of the        first semiconductor layer 22;    -   6 forming a conductive connecting layer 52 on a conductive        substrate 51;    -   7 bonding the conductive substrate 51 with the conductive        connecting layer 52 to the reflecting layer 53;    -   8 removing the temporary substrate to expose one surface of the        second semiconductor layer 24    -   9 forming an extended electrode layer 25 on the exposed surface        of the second semiconductor layer 24;    -   10 forming a first conductive pad 26 on a portion of the        extended electrode layer 25 and the second semiconductor layer        24;    -   11 proceeding a thermal treatment step, such as rapid thermal        annealing (RTA);    -   12 wet etching the second semiconductor layer 24 to form a rough        surface thereon, wherein the features of the rough surface is        described in the previous embodiments, such as FIG. 3A and FIG.        3B;    -   13 forming a second conductive pad 27 on the other side of the        conductive substrate 51.

FIG. 5B shows another embodiment of the present invention. Thelight-emitting device 5 b as shown in FIG. 5B is similar to thelight-emitting device as mentioned above. The distinction is that therough surface is formed on the first semiconductor layer 22.

The manufacturing method for forming the light-emitting device 5 bcomprises the steps of

-   -   1 providing a growth substrate (not shown);    -   2 forming a first semiconductor layer 22, an active layer 23,        and a second semiconductor layer 24 sequentially on the growth        substrate;    -   3 forming a reflecting layer 53 on the second semiconductor        layer 24;    -   4 forming a conductive connecting layer 52 on a conductive        substrate 51;    -   5 bonding the conductive substrate 51 with the conductive        connecting layer 52 to the reflecting layer 53;    -   6 removing the growth substrate to expose one surface of the        first semiconductor layer 22;    -   7 forming an extended electrode layer 25 on the exposed surface        of the first semiconductor layer 22;    -   8 forming a first conductive pad 26 on a portion of the extended        electrode layer 25 and the first semiconductor layer 22;    -   9 proceeding a thermal treatment step, such as rapid thermal        annealing (RTA);    -   10 wet etching the first semiconductor layer 22 to form a rough        surface thereon, wherein the features of the rough surface is        described in the previous embodiments, such as FIG. 3A and FIG.        3B;    -   11 forming a second conductive pad 27 on the other side of the        conductive substrate 51.

FIG. 5C shows another embodiment of the present invention. Thedistinction between the light-emitting device 5 c as shown in FIG. 5Cand the above-mentioned embodiment is that the rough surface is formedinside the light-emitting device 5 c instead of on the outer surface ofthe light-emitting device.

The manufacturing method for forming the light-emitting device 5 ccomprises the steps of

-   -   1 providing a growth substrate (not shown);    -   2 forming a first semiconductor layer 22, an active layer 23,        and a second semiconductor layer 24 sequentially on the growth        substrate;    -   3 forming an extrended electrode layer 25 on the second        semiconductor layer 24;    -   4 proceeding a thermal treatment step, such as rapid thermal        annealing (RTA);    -   5 wet etching the second semiconductor layer 24 to form a rough        surface thereon, wherein the features of the rough surface is        described in the previous embodiments, such as FIG. 3A and FIG.        3B;    -   6 forming a reflecting layer 53 on a conductive substrate 51;    -   7 forming a conductive connecting layer 52 on the reflecting        layer 53;    -   8 bonding the extended electrode layer 25 and the second        semiconductor layer 24 to the reflecting layer 53 by the        conductive connecting layer 52;    -   9 removing the growth substrate to expose one surface of the        first semiconductor layer 22;    -   10 forming a first conductive pad 26 on a portion of the exposed        surface of the first semiconductor layer 22;    -   11 forming a second conductive pad 27 on the other side of the        conductive substrate 51.

FIG. 6 shows a light-emitting device having a lateral structure asanother embodiment of the present invention. The light-emitting device 6and the light-emitting device 5 c each comprises a rough surface insidethe device. The distinction is that the light-emitting device 6 furthercomprises a transparent conductive layer 63 for electrically couplingthe first conductive pad 26 to the second conductive pad 27 and bondingto a transparent substrate 61 by a transparent adhesive layer 62. Atleast one of the transparent adhesive layer 62 and the transparentsubstrate 61 comprises an insulating layer or an insulating structurefor electrically isolating the transparent substrate 61 from thetransparent conductive layer 63, such as forming an insulating layer ona transparent conductive substrate. The material of the transparentconductive layer 63 comprises indium tin oxide (ITO), zinc oxide (ZnO)or thin metal. The material of the transparent adhesive layer 62comprises polyimide (PI), benzocyclobutene (BCB), perfluorocyclobutane(PFCB), epoxy resin, or silicone. The material of the transparentsubstrate 61 comprises sapphire, glass GaP, SiC, or CVD diamond. Thelight-emitting device 6 comprises a transparent bonding structure and atransparent substrate to be capable of extracting light from thesubstrate, and then improve the light extraction efficiency.

The manufacturing method for forming the light-emitting device 6comprises the steps of:

-   -   1. providing a growth substrate (not shown);    -   2. forming a first semiconductor layer 22, an active layer 23,        and second semiconductor layer 24 sequentially on the growth        substrate;    -   3. forming an extended electrode layer 25 on the second        semiconductor layer 24;    -   4. proceeding a thermal treatment step, such as rapid thermal        annealing

(RTA);

-   -   5. wet etching the second semiconductor layer 24 to form a rough        surface thereon, wherein the features of the rough surface is        described in the previous embodiments, such as FIG. 3A and FIG.        3B;    -   6. forming a transparent conductive layer 63 the extended        electrode layer 25 and the second semiconductor layer 24;    -   7. forming a transparent adhesive layer 62 on a transparent        substrate 61;    -   8. bonding the transparent conductive layer 63 to the        transparent substrate 61 by the transparent adhesive layer 62;    -   9. removing the growth substrate to expose one surface of the        first semiconductor layer 22;    -   10. removing a part of the first semiconductor layer 22, the        active layer 23, the second semiconductor layer 24, and the        transparent conductive layer 63 to expose a portion of the        transparent conductive layer 63;    -   11. forming a first conductive pad 26 on the first semiconductor        layer 22;    -   12. forming a second conductive pad 27 on the exposed portion of        the transparent conductive layer 63.

Another alternative embodiment for step 10 to step 12 of the method forforming the light-emitting device 6 is to remove a part of the firstsemiconductor layer 22, the active layer 23, the second semiconductorlayer 24 to expose a portion of the second semiconductor layer 24, andform the second conductive pad 27 on the exposed portion of the secondsemiconductor layer 24.

According to the various embodiments described as above, it is stillunder the scope of the present invention to form the featured roughsurface on both of the first semiconductor layer and the secondsemiconductor layer to further enhance the light extraction efficiency.

It should be noted that the proposed various embodiments are not for thepurpose to limit the scope of the invention. Any possible modificationswithout departing from the spirit of the invention may be made andshould be covered by the invention.

1. An optoelectronic semiconductor device comprising: a substrate; asemiconductor stack disposed on the substrate and having a roughsurface; an electrode layer between the semiconductor stack and thesubstrate; a conductive connecting layer between the semiconductor stackand the substrate; and a first electrode structure overlaying thesemiconductor stack; wherein the rough surface comprises a first regionhaving a first rough topography and a second region having a secondrough topography different from the first rough topography.
 2. Theoptoelectronic semiconductor device according to claim 1, wherein thematerial of the conductive connecting layer comprises a silver paste ora solder metal.
 3. The optoelectronic semiconductor device according toclaim 1, wherein the material of the conductive connecting layercomprises a transparent conductive oxide.
 4. The optoelectronicsemiconductor device according to claim 1, wherein the material of theconductive connecting layer comprises a thin metal.
 5. Theoptoelectronic semiconductor device according to claim 1, wherein adimension of the second region is smaller than a dimension of the firstregion.
 6. The optoelectronic semiconductor device according to claim 1,wherein the first region surrounds the first electrode structure.
 7. Theoptoelectronic semiconductor device according to claim 1, wherein thefirst electrode structure comprises an electrode layer.
 8. Theoptoelectronic semiconductor device according to claim 7, furthercomprising an ohmic contact layer formed between the semiconductor stackand the electrode layer.
 9. The optoelectronic semiconductor deviceaccording to claim 7, wherein the first electrode structure furthercomprises a first conductive pad.
 10. The optoelectronic semiconductordevice according to claim 1, further comprising a second conductive padon a surface of the substrate opposite to the semiconductor stack.